Additional Columns

DDC seems to be a good candidate for our purposes at this time, especially because it accepts additional properties for each column. Could you let me know if we can add data elements to the dictionary while they are not a column on any tables at this time?
If yes, how does it keep the dictionary in synch with the database? Do we lose the additional data elements if we copy back from database again (can we do this; copy back?)
Of course we could create a dummy catchall table and add the extra columns to it; would this cause any problems?